dev-R/brio: add tests

Signed-off-by: Robert Greener <me@r0bert.dev>

dev-R/brio/metadata.xml

@@ -17,4 +17,7 @@ files and provide more explicit control over line endings.</longdescription>
 		<bugs-to>https://github.com/r-lib/brio/issues</bugs-to>
 		<remote-id type="github">r-lib/brio</remote-id>
 	</upstream>
+	<use>
+		<flag name="test">Run the tests</flag>
+	</use>
 </pkgmetadata>